Unfortunately, the design, though acclaimed for its architecture, suffered from important engineering flaws. The soft ground could not support the heavy central stone tower and steeple, which began to subside and lean. By 1920, the tower leaned 1.2 m (3.9 ft) to the south. This defect formed the basis of an important lawsuit (Wardle v. Bethune) often cited as precedent relating to Article 1688 of the Quebec Civil Code.

George Allan Ross designed alterations in 1923 and reconstructed the tower from 1939 to 1940.[7] In 1927, the stone steeple, weighing 1,600,000 kg (3,500,000 lb) was removed. New foundations were poured in 1939, and in 1940, an anonymous donation permitted the construction of a much lighter steeple made of aluminum, molded to simulate the former stone spire. It is 38 m (125 ft) high, attaining a height of 70 m (230 ft) from the ground.[4]

Recent additions to the church include a choir gallery, built in 1980, and the church's third organ, installed in 1981. Notable musicians to have served as the church's organist include Alfred Whitehead (1922–1947) and S. Drummond Wolff (1952–1956).

The organ is opus 77 of Karl Wilhelm, Inc. of Mont-Saint-Hilaire, Quebec. It is a mechanical key and stop instrument with four-manuals, 42 stops and 63 ranks. In 1992, the pedal division was expanded with a 32' Bombarde.

The organ replaced the earlier instrument that served the congregation from 1859. The earlier instrument was constructed by William Hill and Son in London to duplicate an organ given to the congregation by King George III and destroyed in the fire of 1856. The Hill instrument was remodeled and enlarged several on at least five occasions during the tenure of its service. In 1979, the congregation commissioned the mechanical organ and the earlier instrument was sold for parts.[8]

In the 1980s, a vast real estate project was undertaken below the cathedral. The project consisted of a 34-floor skyscraper, Tour KPMG built north of the Cathedral, underground parking, and two levels of retail stores situated beneath the cathedral. For a period in 1987, the Cathedral was supported on stilts while footings for the underground mall, Promenades Cathédrale, were excavated. This project allowed for the linkage of the eastern and western branches of Montreal's underground city, connecting Eaton's (now Les Ailes de la Mode) and The Bay.

Christ Church Cathedral is the regimental church of the Canadian Grenadier Guards. The guards maintain their traditional ties with the church, as well as to McGill University, by marching from the Arts Building on campus, to the cathedral, annually in commemoration of Remembrance Day. The cathedral also houses the guards' retired regimental colours.